Process for the electrolysis of alkali chloride solution

ABSTRACT

The anodic overvoltage and the decomposition of the amalgam during the electrolysis of alkaline chloride solutions in electrolytic cells are reduced by adding to the electrolyte small quantities of one or more compounds selected from the group consisting of the ethers of alcohols or phenols with polyoxyethylenes and of the esters of carboxylic acids with polyoxyethylenes.

United States Patent 191 H Corradi et al.

[ Nov. 19, 1974 PROCESS FOR THE ELECTROLYSIS OF ALKALI CHLORIDE SOLUTIONInventors: Bruno Corradi', Corso ltalia;

Vincenzo Petrillo, Cirie; Giordano Cimarosti, Roverbella, all of ItalyMontecatini Edison S.p.A., Milan, Italy Filed: Aug. 2, 1973 Appl. No.:385,042

Related U.S. Application Data Continuation of Ser. No. 130,472, April 1,1971, abandoned, which is a continuation-in-part of Ser. No. 796,190,Feb. 3, 1969, abandoned.

Assignee:

Foreign Application Priority Data Feb. 6, 1968 Italy 12416/68 U.S. Cl204/98, 204/99, 204/128 Int. Cl. C01d 1/06, COld 1/08 [58] Field ofSearch 204/98, 99, 128

[56] References Cited UNITED STATES PATENTS 3,630,863 12/1971 Jeffery etal. 204/98 Primary Examiner-R. L. Andrews Attorney, Agent, orFirmStevens, Davis, Miller &

I Mosher [5 7] ABSTRACT 12Claims, No Drawings PROCESS FOR THEELECTROLYSIS OF ALKALI v CHLORIDE SOLUTION This is a continuation, ofapplication Ser. No. 130,472, filed Apr. l, 1971 and now abandoned whichin turn was a continuation-in-part of application Ser.

No. 796,190, file Feb. 3, 1969, and now abandoned.

This invention relates to a process for the electrolysis of solutions ofalkaline chlorides. More particularly, this invention has for its objecta process for reducing the anodic overvoltage during the electrolysis ofsolutions of alkaline chlorides in cells having a mercury cathode and indiaphragm cells and for reducing the decomposition of the amalgam duringthe electrolysis of said solutions in cells having a mercury cathode.

It is well known that the voltage that must be applied in practice tosaid cells is definitely in excess of the sum of the electromotive forceof the electrolysis reaction and of the voltage drops due to theresistance of the electrolyte, of the electrodes and of the electricalconnections. One of the main reasons for this voltage excess lies in thegaseous barrier arising from the formation on the anode surface ofrelatively large chlorine bubbles which reduce the active surface of theanode itself.

Another drawback in the operation of cells having a mercury cathodearises from the development of hydrogen caused prevailingly by thepresence of impurities in the brine, which impurities act on the surfaceof the amalgam as active centers for the decomposition of the amalgamitself.

This decomposition, although of relatively little extent, causes howevera useless consumption of current and leads to a contamination of thechlorine produced in the cell, with consequential complications arisingin the liquefaction plant for the produced chlorine.

Furthermore, if the development of hydrogen reaches values exceedingabout 7 percent by volume, explosive mixtures may form.

Thus, one object of this invention is that of reducing the anodicovervoltage during the electrolysis of solutions of alkaline chloridesin electrolytic cells having a mercury cathode and in diaphragm cells.

Still another object of this invention is that of reducing thedecomposition of the amalgam in electrolytic cells having a mercurycathode.

A further object is that of attaining all the objects specified beforealso in the electrolysis operations when carried out under hightemperatures, that is, at temperatures between 70 and 90C.

All these objects, as well as many others, are attained by the processof this invention, according to which the anodic overvoltage (in cellshaving a mercury cathode and in diaphragm cells) and the decompositionof the amalgam (in cells having a mercury cathode) during theelectrolysis of solutions of alkaline chlorides are reduced by adding tothe electrolyte from 2 to 200 ppm of at least one compound selected froma group consisting of alcohol ethers or phenol ethers withpolyoxyethylenes and of esters of carboxylic acids withpolyoxyethylenes.

In the case of ethers of alcohols with polyoxyethylenes, the alcoholsused are generally aliphatic or aromatic alcohols of which the alkylradical contains from 2 to carbon atoms. The aliphatic chain linked tothe alcoholic group may be linear or variously branched. The alcoholsmay contain one or more additional functional groups, and moreparticularly: OH, Cl, Br, F, SO H, SO Me wherein Me is an alkali metal,COOR wherein Ris an alkyl radical containing from one to four carbonatoms, and

wherein R and R are hydrogen or alkyl radicals containing from 1 to 12carbon atoms. Preferably, the alcohols contain from 8 to 20 carbonatoms. Particularly suitable are the aliphatic alcohols containing from12 to 18 carbon atoms.

Some specific examples of suitable alcohols are, for instance, laurylalcohol, oleyl alcohol, stearyl alcohol and phenylethyl alcohol.

The ethers derived from the condensation of such alcohols with ethyleneoxide contain, in general, from 2 to l5O molecules of ethylene oxide foreach molecule of alcohol. Preferably they contain from 10 to moleculesof ethylene oxide for each alcohol molecule. The degree of ethoxylationthat gives the best results depends in part on the nature of theR-radical. Amongst the alcohol ethers with polyoxyethylenes which haveyielded the best results may be listed the monolaurylethers ofpolyethylenglycols containing from 10 to 30 ethoxy groups and themonooleylethers of polyethylenglycols containing from 60 to 120 ethoxygroups.

The ethers of phenols with polyoxyethylenes suited for the purposes ofthis invention may be represented by the general formula:

o-om-cm)..oir

wherein:

R is an alkyl or aralkyl radical having from 1 to 20 carbon atoms and nis between 2 and 40, inclusive.

The alkyl radical R (or the alkyl part of the radical) may be linear orvariously branched.

The radical may contain one or more additional functional groups, inparticular those already specified for the alcohol condensates withethylene oxide.

Preferably, the R radical contains from 8 to 20 carbon atoms.Particularly suitable are the compounds in which R contains from 8 to 13carbon atoms. If R is an alkyl radical, it may for instance be an octyl,nonyl, dodecyl or tridecyl group.'lf it is an aralkyl radical it may,for instance, be a cumyl or methylcumyl group. The radical may be in anortho-, paraor metaposition with respect to the polyethoxy chain.

Because of the method of their preparation these compounds are generallymixtures of numerous isomers and homologues, both as far as the alkylchain is concerned, which may be variously branched, as well as withregard to the position of the R radical with re spect to the ethoxygroup.

Although good results are obtained when all the compounds have a degreeof ethoxylation between 2 and 40, in general those are preferred whichhave a degree of ethoxylation between 5 and 30. Here again, the degreeof ethoxylation which gives best results depends on the nature of the Rradical.

Amongst the compounds having an alkyl R radical which have yielded thebest results may be listed the following:

lst. the mixtures of paraand orthoisomers (e.g., with 90 percent of paraand 10 percent of ortho) of the ethoxy derivatives of nonyl-phenol,having a degree of ethoxylation between 20 and 30, and

2nd. the ethoxy derivatives of iso-octylphenol, having .a degree ofethoxylation between 9 and 10; such products are well known under thetrade name Triton X-lOO.

Amongst the preferred compounds having an aralkyl radical, there may bementioned the derivatives of para-alpha-cumyl-phenol having thefollowing general formula:

wherein: n is between 5 and 25, inclusive.

The esters of carboxylic acids with polyoxyethylenes suitable for thepurposes of thisinvention are compounds having a degree of ethoxylationbetween 200 and 6000, derived from aliphatic or aromatic acidscontaining from 6 to 20 carbonatoms. The aliphatic radical of theseacids may be linear or variously branched. The acids may contain one ormore additional functional groups, and in particular those alreadyspecified previously. Preferably the acids are aliphatic acidscontaining from 12 to 18 carbon atoms. A few specific examples of acidssuitable for the purpose are lauric, oleic, stearic and palmitic acids.

In the place of one single compound or of one single mixture of isomersthere may be used with just as good results mixtures of compounds suchas for instance a mixture of compounds having a differentdegree ofethoxylation derived from the same hydroxy compound or a mixture ofcompounds derived from different hydroxy compounds. Such mixtures ofcompounds may, for instance, include mono(para-alphacumylphenyl)ethersof heptaethylenglycol and of eicosane-ethylenglycol, that is, thederivatives of paraalpha-cumylphenol mentioned above where n=7 andn==20, or the mono(para-alpha-cumylphenyl)ether of heptaethylenglycolmixed with the mono-nonylphenyl ethers of eicosane-ethylene-glycol, thatis, the derivatives of the nonylphenol mentioned above where n=20.

The quantities of additive may be varied within wide limits. Excellentresults are obtained by using quantities between 5 and 20 p.p.m. byweight. The results are, however, just as good when greater quantitiesare used, for instance, from 20 to 200 ppm, although it is not necessaryto make use of these higher quantities. Good results are also obtainedwith lower quantities, for instance with from 2 to 5 p.p.m.

The additives may be used with excellent results at any temperaturebetween room temperature and C.

The feature of being able to use the additives at high temperatures(e.g., 7090C) represents a considerable advantage because said hightemperatures correspond to high current densities and therefore to agreater potentiality of the cells.

The process of this invention may be applied with excellent results toall types of mercury cathode cells, that is, both to the horizontalcathode types and to the vertical cathode types and to all types ofdiaphragm cells as well as to all the types of anodes, that is both tothe graphite anodes and to the metal anodes, for instance titaniumanodes.

When the present process is applied to diaphragm cells, one does notsee, obviously, the particular advantage due to the reduction of thedecomposition of the amalgam.

The additives have proved to be equally efficacious throughout the rangeof current densities that are used in the electrolytic cells, that is inthe range from about 20 to about amp/dm when working with graphiteanodes and from about 20 to about 200 amp/dm when working with metalanodes. The current density is not a critical feature of the process ofthe invention but depends solely upon the characteristics of the cellsemployed.

The additive, which at room temperature may be solid or liquid, may beadded as such to the brine before the introduction thereof into the cellor as solution in water or in the brine.

The solutions used for the purposes of the present invention have ingeneral a concentration between 0.1 to 10 percent by weight. During theadmixture of the additive to the brine, one must ensure an effectivemixing in order to bring about a homogeneous distribution of theadditive in the brine.

The following detailed working examples are given for the purpose ofstill better illustrating the inventive idea:

EXAMPLE 1 The tests were carried out in small experimental cells havingPlexiglass walls, into which were placed in a horizontal position one ortwo graphite anodes at an adjustable distance from the level of themercury that flowed on the bottom of the cell.

The anodic surface amounts to about 2.0 dm The concentration in NaCl ofthe brine fed into the cell amounts to 310 gr/lt (grams per liter): itspH is between 3 and 4. Its NaCl concentration at the outletequals260-270 gr/lt. Its content in impurities is the following:

Turbidity (expressed as SiO,) 10 ppm (parts per million) CaO 0.0l-0.04gr/lt MgO 0.005 gr/lt Fe 0.00l grllt Other metal cations 0.0l ppmSulphate anions, expressed as S0, 2-5 grllt A current density of 70amp/dm was applied. The temperature of the brine at the outlet of thecell was 76C.

The tests were carried out with different infraelectrodic distances,with the following additives:

l. mono(para-alpha-cumylphenyl) ether of heptaethyleneglycol (PCP-7);

For comparative purposes, each test was also repeated without theadditives.

30 minutes after the starting of the cells, their voltage was measuredand the concentration of the hydrogen in the electrolysis gas, whichcontains about 99.0 percent of chlorine by volume, was checked.

These measures were repeated every 15 minutes ,throughout the test,which lasted 3 hours. The conditions, as recorded below in Table l, weremaintained practically constant throughout the test average temperatureof the brine cell: 85C,

current density: 70 amp/dm The brine used was identical with that usedin Example 1 its concentration in NaCl at the outlet of the cell being270 gr/lt.

The experiments were carried out with the following additives:

1 mono-para-alpha-cumylphenyl) thyleneglycol (PCP-7);

2. nonylphenylethers of 30-ethyleneglycol (NF-30),

the mixture containing about 90 percent of paraisomers and percent ofortho isomers;

3. iso-octylphenylether of 9- and IO-ethylenegly'col (IOF-9 and lOF-IO),this product being known under the trade name: Triton X-lOO.

Tests nos. 1, 2 and 4 were carried out with anodes having been inoperation for several months; in the case at the outlet of the ether ofheptaeobserved a better distribution and uniformity in the developmentof gaseous bubbles on the anodes and inside th sqluti t.-. .1

The development of hydrogen was reduced, on the average, by aboutpercent.

It may be noted that the conditions which obtain in .ths sualL inet msnieellsss. stfqflrrsflssaiafa TABLE 1 Percentages by volume of AdditiveConcentration lnfraelectrode Tension in volts in the electi olysis gasin distance without with without with ppm in mm additive additiveadditive additive PCF-7 10 2.5 4.36 4.12 0.8 0.7 PCF-7 10 4.0 4.55 4.320.7 0.6 PCP- 10 2.5 4.35 4.15 0.7 0.6 NF-26 10 2.0 4.56 4.36 0.7 0.6AL-20 10 2.0 4.32 4.15 0.7 0.6 AO-lOO 2.0 4.35 4.15 0.6 0.5

of test no. 2, the cell was very dirty. Test no. 3 was carried out withnew anodes.

30 minutes after starting to feed the cells with the brine containingthe additive, the voltage of each cell and the concentration in hydrogenof the electrolysis gas were measured, the electrolysis gas containingabout 96% by volume of C1 The measurements were repeated every 15minutes ,for a total duration of 8 hours. The resulting values arerecorded below in Table 2 and remained practically constant throughoutthe respective tests.

TABLE 2 Percentages by volume of Number Additive Concentration Tensionin volts H in the electrolysis gas of in without with without with Testppm additive additive additive additive l PCP-7 20 4.58 4.42 1.0 0.6 2PCP-7 10 4.70 4.40 0.9 0.8 3 NF-3O 10 4.65 4.40 1.1 0.9

lOF-lO) .as the decomposition of the amalgam is concerned, the

conditions actually existing in the larger industrial cells in which, onthe contrary, there is found a much stronger decrease in the developmentof hydrogen. This is shown in the following example: 1

EXAMPLE 2 These experiments were conducted on an industrial scale incommercial De Nora cells having the following operationalcharacteristics:

distamaabe n pu assua e;.absattttn..-

g The cells that operated with additive were maini. the ethers ofalcohols with polyoxyethylenes tained in a condition of greatercleanliness. which R a. are derived from alcohols selected between all-EXAMPLE 3 phatic and aromatic ones and having from 8 to 20 carbon atoms,and

The tests of this example were carried out in pilot scale De Nora cellsfitted out with dimentionally stable anodes manufactured by-Permelec.These anodes are made of titanium coated with metallic oxides such asruthenium, iridium, tantalum and titanium oxides (for 10 a descriptionof said kind of anodes, see, for instance,

b. contain from 2 to 150 molecules of ethylene oxide for each moleculeof alcohol, ii. the ethers of phenols with polyoxyethylenes having thefollowing formula:

'Dutch Patent Application No. 68/ 17957). The exact R composition of thecoating is not specified by the manufacturer.

The whole anodic surface amounted to about 54.0 dm o-orr,-orr, norr Theoperational characteristics were: distance between anodes and cathode:about 3 mm;

. wherein average temperature of the brine at the cell outlet: 0 a. R isa radical selected between alkyl and aralkyl 85C; and has from 1 tocarbon atoms, and current density: 125 (test 1) and 150 (test ,2) b. nis between 2 and 40, inclusive,

amp/dm iii. the esters of carboxylic acids with polyoxyethy- The brineused was identical with that used in Examlenes ple 1, its concentrationin NaCl at the outlet of the cell which being 290 gr/lt. a. are derivedfrom acids selected between ali- The experiments were carried out withnonylphenphatic and aromatic ones and having from 6 to ylethers of-ethyleneglycol (NF-30), the mixture 20 carbon atoms, and containingabout 90 percent of para-isomers and 10 b. contain from 200 to 6000ethylene oxide molepercent of ortho-isomers. 30 cules for each moleculeof acid.

Thirty minutes after starting to feed the cells with 2. The process ofclaim 1, wherein the ethers of alcobrine containing the additives, thevoltage of the cell hols with polyoxyethylenes contain from 10 to 120and the concentration in hydrogen of the electrolysis molecules ofethylene oxide for each molecule of alcogas were measured, theelectrolysis gas containing hol.

about 97 percent by volume of Cl 3. The process of claim 2, wherein theethers of alco- The measurements were repeated every 2 hours for holswith polyoxyethylenes are derived from alcohols a total period of 8days. having from 12 to 18 carbon atoms.

The resulting values are recorded in Table 3. They 4. The process ofclaim 3, wherein the alcohol is seremained practically constantthroughout the respeclected from the group consisting of lauryl alcohol,oleyl tiyelests V w n alcohol, stearyl alcohol and phenylethyl alcohol.

TABLE 3 Percentages by volume of Number Additive Concentration CurrentTension in volts H in the electrolysis gas of v in Density without withwithout with Test ppm amp/dm additive additive additive additive l NF-3010 125 3.90 3.74 0.9 0.6 2 NF-30 I0 150 4.03 3.85 0.9 0.6

From an examination of Table 3, it can be seen that 5. The process ofclaim 1, wherein the R radicalof also in this case there was aconsiderable drop (0.16 the ethers of phenols with polyoxyethylenescontains 0.18 volt) in anodic potential. It can also be seen that from 8to 20 carbon atoms and n is between 5 and 30,

the effectiveness of the additives is not lowered by an inclusive.increase in the current density as a higher drop (0.l8 6. The process ofclaim 5, wherein R contains from volt) has been reached with the higherdensity (150 8 to 13 carbon atoms.

p l 7. The process of claim 6, wherein R is selected from Thedevelopment of hydrogen was reduced on the the group consisting ofoctyl, nonyl, dodecyl, tridecyl, average, by about 3 3 percent. cumy]and methylcumyL What claimed 8. The process of claim 1, wherein thecarboxylic 1. In a process for the electrolysis of alkaline chloride bsolutions in mercury cathode cells and diaphragm cells, gf fi ahphancaclds havmg from 12 to 18 car on the improvement comprising reducing theanodic overvoltage in both kinds of cells and the decomposition of TheProcess of lem 1 8,Wherel n the acid 15 selecteg the amalgam in mercurycathode cells during the elecfl p conslstmg of laune, Olele, Steamtrolysis by adding to the electrolyte from 2 to 200 ppm Palmmc acldof atleast one compound selected from the group con- 10. The process of claim1, wherein the aliphatic or sisting of, aromatic alcohol and acidmoieties contain one or m or e aiafiofia l O H; Cl, Br, F, SO H, SO Megroupsin which Me is an alkali radical con- Q M e CQQIia Q g H tainingfrom one to four carbon atoms, and

R1 I I R1 r N/ N groups in which Me is an alkaline metal, R is an alkylgroups in which R, and R are hydrogen or alkyl radiradical containingfrom 1 to 4 carbon atoms, and R gals tai i from 1 to 12 carbon atoms.and 2 are hydrogen alkyl Tadlcals comammg from 12. The process of claim1, wherein from 5 to 20 ppm 1 to 12 carbon atoms. b ht f 10 d 11. Theprocess of claim 1, wherein the R radical y 0 a a ls emp ye

1. IN A PROCESS FOR THE ELECTROLYSIS OF ALKALINE CHLORIDE SOLUTIONS INMERCURY CATHODE CELLS AND DIAPHRAGM CELLS, THE IMPROVEMENT COMPRISINGREDUCING THE ANODIC OVERVOLTAGE IN BOTH KINDS OF CELLS AND THEDECOMPOSITON OF THE AMALGAM IN MERCURY CATHODE CELL DURING THEELECTROLYSIS BY ADDING TO THE ELECTROLYTE FROM 2 TO 200 PPM OF AT LEASTONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF, I. THE ETHERS OFALCOHOLS WITH POLYOXYETHYLENES WHICH A. ARE DERIVED FROM ALCOHOLSSELECTED BETWEEN ALIPHATIC AND AROMATIC ONES AND HAVING FROM 8 TO 20CARBON ATOMS, AND B. CONTAIN FROM 2 TO 150 MOLECULES OF ETHYLENE OXIDEFOR EACH MOLECULE OF ALCOHOL, II. THE ETHERS OF PHENOLS WITHPOLYOXYETHYLENES. HAVING THE FOLLOWING FORMULA:
 2. The process of claim1, wherein the ethers of alcohols with polyoxyethylenes contain from 10to 120 molecules of ethylene oxide for each molecule of alcohol.
 3. Theprocess of claim 2, wherein the ethers of alcohols with polyoxyethylenesare derived from alcohols having from 12 to 18 carbon atoms.
 4. Theprocess of claim 3, wherein the alcohol is selected from the groupconsisting of lauryl alcohol, oleyl alcohol, stearyl alcohol andphenylethyl alcohol.
 5. The process of claim 1, wherein the R radical ofthe ethers of phenols with polyoxyethylenes contains from 8 to 20 carbonatoms and n is between 5 and 30, inclusive.
 6. The process of claim 5,wherein R contains from 8 to 13 carbon atoms.
 7. The process of claim 6,wherein R is selected from the group consisting of octyl, nonyl,dodecyl, tridecyl, cumyl and methylcumyl.
 8. The process of claim 1,wherein the carboxylic acids are aliphatic acids having from 12 to 18carbon atoms.
 9. The process of claim 8, wherein the acid is selectedfrom the groups consisting of lauric, oleic, stearic and palmitic acid.10. The process of claim 1, wherein the aliphatic or aromatic alcoholand acid moieties contain one or more additional -OH, -Cl, -Br, -F,-SO4H, -SO4Me, -COOR and
 11. The process of claim 1, wherein the Rradical contains one or more -OH, -Cl, -F, -Br, -SO4H, -SO4Me groups inwhich Me is an alkali radical containing from one to four carbon atoms,and
 12. The process of claim 1, wherein from 5 to 20 ppm by weight ofadditive is employed.